The present invention relates to a drill steel for percussion drilling having four longitudinally extending and circumferentially spaced passages for removal of cuttings.
Usually, the now used drill steels for percussion drilling, in the mining industry as well as for different kinds of contract work, are either round or hexagonal. The earlier rather usual square shape with higly bevelled corners is now seldom used. Drill steels of these types are disclosed in for instance U.S. Pat. No. 2,733,943.
During recent years hydraulic rock drilling machines are to an increasing extent replacing pneumatic rock drilling machines in percussion drilling of this type. The result of such a change is that the drilling velocity is highly increased, roughly doubled, i e in the same time as one meter was drilled by means of a pneumatic rock drilling machine now two meters are drilled by means of a hydraulic rock drilling machine. Due to the roughly doubled drilling rate, thus, the removal of cuttings per time unit has to be doubled.
In small hole drills for percussion drilling in concrete, brock, stone and similar material it has been proposed to provide the drill with a plurality of concave grooves along which the drilling dust is transported. The diameter of the drill basically coincides with the diameter of the bore hole. Therefore, the primary object of this drill design is to form the convex portions between the concave grooves such that a friction as small as possible does arise against the bore hole wall at the same time as straight holes are produced. The removal of drilling dust and the stresses in the steel, then, are in no way critical factors. Drills of the last-mentioned type are disclosed in for instance U.S. Pat. No. 1,666,898 and U.S. Pat. No. 2,217,202.
The object of the present invention is to provide a drill steel which has an enlarged space for drillings compared to that in conventional drill steels.
Another object of the invention is to provide a drill steel which, in comparison with conventional drill steels, for the same resistance to bending has less material consumption.
A further object of the invention is to provde a drill steel which is well adapted to be twisted so as to create auger characteristics, which often is of advantage in drilling operations in loose kinds of rocks and in non-homogenous or cracked rock formations.
A still further object of the invention is to provde a drill steel which makes possible a collar-shank design which is favourable with respect to arising stresses.